Oh. Looks just good But you have one big problem with colors and shadows. You haven't any shadow under combobox, and mixing red, blue, and some shades of gray doesn't looks very good You haven't any static pretty color scheme, but it also looks very good in concept as GUI-Elements

Update: Added Custom Text Boxes (CustomEdits analog, but with custom design)
- It can be fully transparent, and can be putted on some your-own objects
- Added functions to get caret selection parameters
For current time its not merged in win.lua, cuz now testing for bugs. You also can send me bug reports.
Note: This boxes will never get fonts for memo boxes, because coefficient of difference between two lines are different for all fonts.
Screenshot: (notice that this style is not recommending to use in current windows system style, but it demonstrate how does them looks like)
And, of course, this can be overload your CPU, because it's GUI In future, I hope, I'll port this system to DX, but for now I haven't any ideas how to make on them layering and hiding parts of images in some frames (for scroll panes, for example)

Your calculation method can't be used here, because it needs to update position every time - every frame will be exec function "guiSetPosition", and it will have more lags, because this fuction executes in onClientRender, and it haven't any optimizations.

I know about this troubles. One of the reasons is events, like OnClientRender and OnClientCursorMove. In this events there is too many calculations per frame - getting and setting gui positions. And I haven't any ideas how to fix this, cuz this events must be as main events of system, used to moving/resizing functions, widget animations and etc.

Give me example, where (or on what widget) you moving mouse and CPU usage is overloads. Is it on all widgets?
Cuz I have i5-7200U, and U series are for laptops, and I haven't loading more than 20% of this resource.